This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the presently described embodiments. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present embodiments. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
In the exploration of oil, gas and geothermal energy, drilling operations are used to create boreholes, or wells, in the earth. Drill rigs are typically used for such operations, and drill rigs used in subterranean exploration must be transported to the locations where drilling activity is to be commenced. Adding to the complexity, drill rigs are typically large, complex pieces of machinery that generally must be disassembled for transport and then reassembled at the destination. In a majority of these transport scenarios, the drill rigs are moved by truck and trailer.
The process for assembling the multitude of parts and components of a drill rig for drilling operations is typically known in the industry as “rig up.” During rig up, crews may utilize cranes, rig up trucks, forklifts, and other specialized equipment for moving the parts of the drill rig into place. The process may be very time consuming, and may take several days to complete, depending on the type of rig being assembled and problems encountered during the process. During the rig up process, no drilling work is able to be performed. This adds to the overall cost of the drilling process in terms of crew and equipment expenses. As the drilling process cannot begin until the drill rig has been fully assembled, it is generally desirable to complete the rig up process as quickly and efficiently as possible, thereby minimizing this downtime. However, rig up is a particularly dangerous component of the drilling process, and the speed of the rig up may not be increased at the sacrifice of safety to the drilling crew.
Once drilling work has been completed at a particular well, the rig up process is performed in reverse order (“rig down”) to substantially disassemble the drill rig for transport and rig up at a different location. As expected, the rig down process may require roughly the same amount of time as the rig up process and further adds to downtime and costs for operating a drill rig. While it is imperative that such downtime also be minimized, it cannot be done at the sacrifice of the safety of the drilling crew.
A particularly time consuming and labor intensive task during the rig up and rig down process is the transport and handling of the blowout preventer (“BOP”) stack. As known in the oil field services industry, a BOP is a large, specialized valve installed in redundant, serial stacks that is used to seal, control and otherwise monitor the flow of liquids and gases out of oil and gas wells. Due to the extreme pressures produced by subterranean hydrocarbons, BOP stacks may have a 13″ or greater bore diameter and be rated for working pressure up to and exceeding 10,000 psi. The BOP stack is installed at the wellhead beneath the drill floor so as to control the flow of fluids entering and exiting the well. Additionally, downhole equipment must pass through the BOP stack to be placed downhole. Because the BOP stack is the last line of defense in preventing a blowout, it is critical to the overall safety of the drill rig.
As understood from the above discussion, several individual BOPs are usually stacked on top of one another to form a “BOP stack.” Such stacks may be several meters tall and weigh tens of thousands of pounds. Thus, BOP stacks pose a significant challenge during transportation and positioning during the rig up and rig down process. BOP stacks are at least partially disassembled for transport on trucks, as there is no practical way to transport a fully assembled BOP stack. This disassembly and subsequent reassembly process requires a significant amount of time that adds to the overall time required for rig up and rig down.
Once the BOP stack is assembled, it must be positioned under the rig floor directly over the wellhead. This procedure is also difficult and time consuming because the large BOP stack must be precision located underneath a previously erected drill rig and centered on the axis of the well. Such careful placement requires fine adjustment in at least two horizontal directions. The BOP stack may also need adjustment in the vertical direction due to potential elevation differences at the wellhead. Finally, the BOP stack must be rotated into alignment at the wellhead with one of several connectors which secure the BOP stack to the wellhead.
Most BOP handling systems and methods currently being used involve transferring the BOP stack from one piece of equipment to another, such as from a skid to an overhead lifting system. Many of these overhead lifting systems, such as cranes or trolleys, involve lifting and suspending the BOP, which consumes significant amounts of time and resources to perform safely. When the BOP is lifted in such a manner, it is unwieldy and difficult to maneuver due to the precarious nature of suspending such a heavy load. The lifting of a BOP presents particular safety concerns to the crew working around it, as a mishap and slip of the BOP from the lifting assembly may severely injure crew members.
Prior art provides a two piece lifting assembly that is assembled around the stack. It requires alignment of two separate lifting assemblies around the BOP stack. Prior art pins are large and horizontally mounted, and are thus difficult to install and not held in place by gravity.
Thus, there remains a need for a BOP lifting apparatus that will increase the efficiency and safety of the handling of a BOP stack during rig up, rig down and transport operations. There additionally remains a need for a BOP stack lifting apparatus that can remain stable in the event of a failure or breakage in cables used in the lifting process.
The various embodiments of the present invention disclosed herein address one or more of the problems set forth above.